Diesel engines and other lean-burn engines or power plants are operated at higher than stoichiometric air to fuel mass ratios for improved fuel economy. Such lean-burning engines produce a hot exhaust with a relatively high content of oxygen and nitrogen oxides (NOx). The temperature of the exhaust from a warmed-up diesel engine is typically in the range of 200° C. to 400° C. and has a representative composition, by volume, of about 10-17% oxygen, 3% carbon dioxide, 0.1% carbon monoxide, 180 ppm hydrocarbons, 235 ppm NOx and the balance nitrogen and water. These NOx gases, typically comprising nitric oxide (NO) and nitrogen dioxide (NO2), are difficult to reduce to nitrogen (N2) because of the high oxygen (O2) content in the hot exhaust stream.
Co-pending patent application, docket number GP-305427, titled Reforming Diesel Fuel for NOx Reduction, and assigned to the assignee of this invention, discloses a method of fractionating diesel fuel and reforming the fractionated vapor for use in the selective catalytic reduction of NOx (including NO and NO2) in an exhaust from a lean burn combustion source. The fractionated diesel fuel vapor is reformed to yield relatively low molecular weight oxygenated hydrocarbons using air plasma produced in a nonthermal plasma reactor. The reformed material is added to the exhaust to provide oxygenated hydrocarbon reactants for catalytic reduction of NO2. A separate side stream of ozone-containing air plasma is also added to the exhaust for oxidation of NO to NO2.
The subject invention provides apparatus and a continuous operating method for nonthermal plasma reforming of diesel fuel hydrocarbons.